Silicon nitride etching composition and method

ABSTRACT

Compositions useful for the selective removal of silicon nitride materials relative to polysilicon, silicon oxide materials and/or silicide materials from a microelectronic device having same thereon are provided. The compositions of the invention are particularly useful in the etching of 3D NAND structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patent application Ser. No. 16/681,449 which claims the benefit under the provisions of 35 U.S.C. § 119 of U.S. Provisional Patent Application No. 62/767,904 filed Nov. 15, 2018, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a composition and method for selectively etching silicon nitride in the presence of silicon oxide, polysilicon and/or metal silicides, and more particularly to a composition and method for effectively and efficiently etching a layer of silicon nitride at a high etch rate and with high selectivity with respect to exposed or underlying layers of silicon oxide, polysilicon and/or metal silicides, particularly in a multilayer semiconductor wafer structure.

BACKGROUND OF THE INVENTION

There is a continued need for improved microelectronic device performance there is a continued emphasis on decreasing device dimensions, which provides the dual advantages of dramatically increasing device density as well as improving device performance. Device performance is improved because decreased device dimensions result in shorter paths that need to be traveled by charge carriers, e.g., electrons.

For example, Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFET) gate electrodes have as electrical points of contact the gate surface and the source and drain regions. The distance between the source and drain regions forms the channel length of the gate electrode, and as such, by decreasing device dimensions the channel length is concomitantly decreased. The result is that the switching speed of the device is increased.

It is self-evident that reducing device dimensions results in increased packaging density of devices on a microelectronic device chip. This increased packaging density brings with it sharp reductions in the length of the interconnect paths between devices, which reduces the relative negative impact (such as resistive voltage drop, cross talk or RC delay) that these interconnect paths have on overall device performance.

Such requirements however cause problems of increased parasitic capacitance, device contact resistance (gate, source and drain contacts in MOSFET devices), and tight tolerance of pattern definition. For very small sub-micron or sub-half-micron or even sub-quarter-micron modern silicon devices, the conventional photolithographic technique for patterning contacts will not meet the required tolerance of critical dimensions. Methods that have been explored to improve resolution and feature size include the formation of a self-aligned poly-silicon (poly-Si) gate structure, which helps to solve the problem of critical dimension tolerance. Using this method, the contact points that are formed for the source and the drain of the gate electrode self-align with the poly-Si gate.

One problem encountered during the formation of self-aligned gate structures has been the selective removal of silicon nitride materials relative to polysilicon, silicon oxide and/or metal silicide materials. For example, during the anisotropic etching of the silicon nitride layer covering the gate electrodes, the underlying silicon oxide layer and silicon substrate are often damaged as well, causing a deteriorated reliability of a semiconductor device.

Conventional wet etching techniques for selectively removing silicon nitride (Si₃N₄) have utilized hot (approximately 145-180° C.) phosphoric acid (H₃PO₄) solutions with water, typically 85% phosphoric acid and 15% water (by volume). Using fresh hot phosphoric acid, the typical Si₃N₄:SiO₂ selectivity is about 40:1. Advantageously, as the nitride layer is removed, hydrated silicon oxide forms, which consistent with Le Chatelier's principle, inhibits the additional removal of silicon oxide from the device surface; thus selectivity gradually increases with use. Disadvantages associated with the use of hot phosphoric acid etches include the corrosion of metal silicide materials, e.g., gate contact materials, the etching of silicon oxide, and process control due to the difficultly associated with maintaining a specific amount of water in the process solution. In addition, hot phosphoric acid has been a difficult medium to adapt to single wafer tools, which have become increasingly preferred by many manufacturers.

Another way to selectively remove silicon nitride includes the use of a composition including hydrofluoric acid, however, said compositions also remove silicon oxides. A Si₃N₄:SiO₂ selectivity of about 10:1 can be achieved through dilution; however, the etch rate of silicon nitride is compromised or above-ambient pressure must be used. Still another process to remove silicon nitride includes the dry etch removal using halogenated gaseous species; however, the Si₃N₄:SiO₂ selectivity ratio is even worse than that obtained using the aforementioned wet etch processes.

3D-NAND structures in development today at all the major memory chip manufacturers require high-selectivity etching of silicon nitride (SiN) out of high aspect ratio “slits” defined by oxide (PETEOS). In the regular hot phosphoric acid “hot phos” process the selectivity is controlled by pre-dissolving a certain amount of nitride. The dissolved silicon nitride is converted into slightly soluble oxide; the same happens during etching, but the oxide soon starts depositing near the slits' openings, eventually blocking them. See also US 2017/0287725, in particular FIG. 1D, which shows an illustration where the deposition of colloidal silica tends to “pinch off” the gaps or trenches in the microelectronic device. As a result, the process window of pre-etch oxide concentration is very narrow, difficult to control, and the etch bath has to be replaced very often. Oxide re-deposition rate thus needs to be minimized.

In addition, the deep slits take a long time to etch (typically ≥1 hr). Addition of HF in small amounts increases etch rates, but also polymerization of soluble silica species and consequently oxide re-deposition rates. Furthermore, the volatility of HF and related fluorinated species causes process control difficulties.

In planar NAND technology, scaling is driven mostly by lithography. In scaling 3D NAND, extreme precision and process repeatability is required to create complex 3D structures with very high-aspect-ratio (HAR) features. Therefore, achieving success with 3D NAND requires innovative patterning solutions that minimize variability. (See Overcoming Challenges in 3D NAND Volume Manufacturing. Solid State Technology website: http://electroig.com/blog/2017/07/overcoming-challenges-in-3d-nand-volume-manufacturing/)

Precision in etching extreme HAR features is critical for optimizing channel holes and trenches for cell access, as well as its unique staircase structure architecture, which connects the cells to surrounding CMOS circuitry for reading, writing, and erasing data. If the vertical pitch of the memory stack is around 50 nm, then a 96 layer stack is on the order of 4.8 μm high. This corresponds to a challenging aspect ratio of −100:1.

Additionally, as multilayer stack heights increase, so does the difficulty in achieving consistent etch and deposition profiles at the top and the bottom of the memory array. For example, given a ratio of 100:1, the selective removal of Si₃N₄ in the memory stack becomes a wet-etch challenge. The difficulty is removing the Si₃N₄ consistently at the top and the bottom of the stack and across the wafer, without etching any of the Sift. Below 96 layers, this task is performed using hot phosphoric acid (−160° C.); however, at 96 layers and above, a specially formulated wet etch chemistry is needed to improve process margin.

SUMMARY OF THE INVENTION

In one aspect, the invention provides compositions useful in etching a substrate having a surface comprising silicon nitride and silicon oxide, with selectivity for etching the silicon nitride relative to the silicon oxide. The composition comprises phosphoric acid, at least one silane compound chosen from alkylamino alkoxy silanes and alkylamino hydroxyl silanes, a solvent comprising water, and optionally a fluoride compound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 show a comparison of several examples of the invention in terms of etch rates versus Si loading. Silicon nitride and silicon oxide etch rates were measured using CVD silicon nitride films and PECVD silicon oxide films. Silicon oxide films were exposed to the etching formulation for 4 hours so that the small amount of film loss could be measured. Silicon nitride films were etched for 5 minutes and 10 minutes. Film thicknesses were measured before and after processing by spectroscopic ellipsometry and these thicknesses were used to calculate etch rates.

Specifically, the figures depicts the following:

FIG. 1 depicts a graph that shows etch rates as a function of Si Loading

FIG. 2 depicts a graph displaying the etch rates as a function of Si loading

FIG. 3 depicts graph displaying the etch rates in 85% phosphoric acid as a function of Si loading

FIG. 4 depicts a graph showing selectivity (“example B”), (“example A”) and 85% H₃PO₄.

FIG. 5 shows schematically a structure of an exemplary substrate as described, before and after a selective etching step as also described.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present invention relates to compositions which are useful in the selective removal of silicon nitride relative to polysilicon (poly-Si) and silicon oxide material deposited from a silicon oxide precursor source, and hence are useful as wet etchants for at least partial removal of silicon nitride material from a microelectronic device. Metal silicide materials that may be present should not be substantially corroded by said removal compositions.

The invention also provides methods, processes, and systems for using the wet etching compositions to remove silicon nitride from a substrate containing silicon nitride and silicon oxide. The compositions can produce an advantageously high etch rate of silicon nitride, an advantageously high selectivity of silicon nitride relative to silicon oxide, or an advantageous balance of these performance properties.

For ease of reference, “microelectronic device” corresponds to semiconductor substrates, including 3D NAND structures, flat panel displays, and microelectromechanical systems (MEMS), manufactured for use in microelectronic, integrated circuit, or computer chip applications. It is to be understood that the term “microelectronic device” is not meant to be limiting in any way and includes any substrate that includes a negative channel metal oxide semiconductor (nMOS) and/or a positive channel metal oxide semiconductor (pMOS) transistor and will eventually become a microelectronic device or microelectronic assembly.

As used herein, “suitability” for removing silicon nitride material from a microelectronic device having such nitride material thereon corresponds to at least partial removal of silicon nitride material from the microelectronic device.

As used herein, “silicon nitride” and “Si₃N₄” correspond to pure silicon nitride (Si₃N₄) as well as impure silicon nitride including hydrogen, carbon and/or oxygen impurities in the crystal structure.

As used herein, “silicon oxide” refers to thin films made of silicon oxide (SiO_(x)), e.g., SiO₂, “thermal oxide” (ThO_(x)), and the like. The silicon oxide can be placed on the substrate by any method, such as by deposition via chemical vapor deposition from TEOS or another source, or by being thermally deposited. The silicon oxide generally contains a commercially useful low level of other materials or impurities. The silicon oxide may be present as part of a microelectronic device substrate as a feature of the microelectronic device, for example as an insulating layer.

As used herein, “at least partial removal of silicon nitride material” corresponds to the removal of at least a portion of the exposed silicon nitride layer. For example, partial removal of silicon nitride material includes the anisotropic removal of a silicon nitride layer that covers/protects the gate electrodes to form a Si₃N₄ sidewall. It is also contemplated herein that the compositions of the present invention may be used more generally to substantially remove silicon nitride material relative to poly-silicon and/or silicon oxide layers. In those circumstances, “substantial removal” is defined in one embodiment as at least 90%, in another embodiment at least 95%, and in yet another embodiment at least 99% of the silicon nitride material is removed using the compositions of the invention.

As used herein, “about” is intended to correspond to +/−5% of the stated value.

As used herein, “metal silicide” corresponds to any silicide including the species Ni, Pt, Co, Ta, Mo, W, and Ti, including but not limited to TiSi₂, NiSi, CoSi₂, NiPtSi, tantalum silicide, molybdenum silicide, and tungsten silicide.

“Silicic acid” is a general name for a family of chemical compounds of silicon, hydrogen, and oxygen, with the general formula [SiO_(x)(OH)_(4-2x)]_(n), and includes the compounds metasilicic acid ((H₂SiO₃)_(n)), orthosilicic acid (H₄SiO₄), disilicic acid (H₂Si₂O₅), and pyrosilicic acid (H₆Si₂O₇). Silicic acid can be obtained in many ways well known to those skilled in the art, e.g. by hydrating fine silica powder (preferably 1 μm diameter or less), alkoxysilanes (e.g., tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetra-n-propoxysilane, tetra-n-butoxysilane), alkoxysilanes with amino groups (e.g., aminotriethoxysilane, hexaethoxydisilazane), alkoxysilanes with one or more halogen or pseudohalogen groups (e.g., triethoxychlorosilane, triethoxyfluorosilane, triethoxy(isocyanato)silane, diethoxydichlorosilane), or combinations thereof. For ease of reference, “alkoxysilane” will hereinafter be used to include alkoxysilanes, alkoxysilanes with amino groups and alkoxysilanes with one or more halogen or pseudohalogen groups.

As described herein, the silicon oxide layer may be deposited from a silicon oxide precursor source, e.g., TEOS, or may be thermally deposited silicon oxide. Other typical low-κ materials “low-k dielectric material” corresponds to any material used as a dielectric material in a layered microelectronic device, wherein the material has a dielectric constant less than about 3.5. In certain embodiments, the low-κ dielectric materials include low-polarity materials such as silicon-containing organic polymers, silicon-containing hybrid organic/inorganic materials, organosilicate glass (OSG), TEOS, fluorinated silicate glass (FSG), silicon dioxide, silicon oxycarbide, silicon oxynitride, silicon nitride, carbon-doped oxide (CDO) or carbon-doped glass, for example, CORAL™ from Novellus Systems, Inc., BLACK DIAMOND™ from Applied Materials, Inc. (e.g., BD1, BD2, and BD3 designations for PECVD) SiLK™ dielectric resins from Dow (polymers based on crosslinked polyphenylenes by reaction of polyfunctional cyclopentadienone and acetylene-containing materials; see, for example, U.S. Pat. No. 5,965,679, incorporated herein by reference), and NANOGLASS™ of Nanopore, Inc, (Silica aerogel/xerogel (known as nanoporous silica), and the like. It is to be appreciated that the low-κ dielectric materials may have varying densities and varying porosities.

The compositions of the present invention must possess good metal compatibility, e.g., a low etch rate on the interconnect metal and/or interconnector metal silicide material. Metals of interest include, but are not limited to, copper, tungsten, cobalt, molybdenum, aluminum, tantalum, titanium and ruthenium. Silicides of interest include any silicide including the species Ni, Pt, Co, Ta, Mo, W, and Ti, including but not limited to TiSi₂, NiSi, CoSi₂, NiPtSi, tantalum silicide, molybdenum silicide, and tungsten silicide.

Compositions of the invention may be embodied in a wide variety of specific formulations, as hereinafter more fully described.

In all such compositions, wherein specific components of the composition are discussed in reference to weight percentage ranges including a zero lower limit, it will be understood that such components may be present or absent in various specific embodiments of the composition, and that in instances where such components are present, they may be present at concentrations as low as 0.001 weight percent, based on the total weight of the composition in which such components are employed.

The composition includes aqueous phosphoric acid (e.g., concentrated phosphoric acid) in an amount that is effective to produce desired etching of silicon nitride. The term “aqueous phosphoric acid” refers to an ingredient of the composition that is mixed or combined with other ingredients of the composition to form the composition. The term “phosphoric acid solids” refers to the non-aqueous component of an aqueous phosphoric acid ingredient, or of a composition that is prepared from aqueous phosphoric acid ingredient.

The amount of phosphoric acid solids contained in a composition can be an amount that, in combination with the other materials of an etching composition, will provide desired etching performance, including desired silicon nitride etch rate and selectivity, which typically requires a relatively high amount (concentration) of phosphoric acid solids. For example, an etching composition can contain an amount of phosphoric acid solids that is at least about 50 weight percent based on total weight of the composition, e.g., at least 70, or at least about 80 or 85 weight percent phosphoric acid solids based on total weight of the composition.

To provide a desired amount of phosphoric acid solids, the composition may contain “concentrated” phosphoric acid as an ingredient that is mixed or combined with other ingredients (one ingredient optionally being water, in some form) to produce the composition. “Concentrated” phosphoric acid refers to an aqueous phosphoric acid ingredient that contains a high or maximum amount of phosphoric acid solids in the presence of a low or minimum amount of water and substantially no other ingredients (e.g., less than 0.5 or 0.1 weight percent of any non-water or non-phosphoric acid solids materials). Concentrated phosphoric acid can typically be considered to have at least about 80 or 85 weight percent phosphoric acid solids in about 15 or 20 weight percent water. Alternately, the composition may be considered to include an amount of concentrated phosphoric acid that is diluted with water, meaning for example concentrated phosphoric acid that has been diluted with an amount of water before or after being combined with other ingredients of the etching composition, or an equivalent formed in any manner. As another alternative, an ingredient of the composition can be concentrated phosphoric acid or a diluted phosphoric acid, and the etching composition can contain an additional amount of water that is provided to the composition either as a component of a different ingredient or as a separate water ingredient.

As an example, if concentrated phosphoric acid is used to form the composition, the amount of concentrated phosphoric acid (85 weight percent, in water) can be an amount that is at least 60, e.g., at least 80 or at least 90, 93, 95, or at least 98 weight percent of the composition, based on total weight of the composition.

The compositions can comprise, consist of, or consist essentially of the recited ingredients and any combination of optional ingredients. As a general convention throughout the present description, the composition as described, or an ingredient or component thereof, that is said to “consist essentially of” a group of specified ingredients or materials refers to a composition that contains the specified ingredients or materials with not more than a low or insignificant amount of other ingredients or materials, e.g., not more than 5, 2, 1, 0.5, 0.1, or 0.05 parts by weight of other ingredients or materials. For example, a composition that contains materials that consist essentially of: aqueous phosphoric acid, at least one silane compound chosen from (i) alkylamino alkoxysilanes and (ii) alkylamino hydroxyl silanes, and a solvent comprising water, and optional ingredients as described, means a composition that contains these ingredients and not more than 5, 2, 1, 0.5, 0.1, or 0.05 parts by weight of any other dissolved or un-dissolved material or materials (individually or as a total) other than the identified materials.

As used herein, “fluoride compound” corresponds to species including ionic fluoride ion (F⁻) or covalently bonded fluorine. It is to be appreciated that the fluoride species may be included as a fluoride species or generated in situ. In certain embodiments, this compound capable of generating the fluoride ion will be derived from HF, monoflurophosphoric (MFPA), difluorophosphoric (DFPA) or hexafluorophosphoric acid. In concentrated phosphoric acid compositions, HF will exist mostly in the form of monofluorophosphoric acid (MFPA). In certain embodiments, the low-volatility MFPA or DFPA may be used directly in the compositions in order to simplify addition and blending. In other embodiments, the fluoride compound may be chosen from CsF and KF. In other embodiments, the fluoride compound may be chosen from tetramethylammonium hexafluorophosphate; ammonium hexafluorophosphate; ammonium fluoride; ammonium bifluoride; quaternary ammonium tetrafluoroborates and quaternary phosphonium tetrafluoroborates having the formula NR′₄BF₄ and PR′₄BF₄, respectively, wherein each R′ may be the same as or different from one another and is chosen from hydrogen, straight-chained, branched, or cyclic C₁-C₆ alkyl (e.g., methyl, ethyl, propyl, butyl, pentyl, hexyl), and straight-chained or branched C₆-C₁₀ aryl (e.g., benzyl); tetrabutylammonium tetrafluoroborate (TBA-BF₄); and combinations thereof. In certain embodiments, the fluoride compound is selected from ammonium fluoride, ammonium bifluoride, quaternary ammonium tetrafluoroborates (e.g., tetramethylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, tetrapropylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate), quaternary phosphonium tetrafluoroborates, or combinations thereof. In certain embodiments, the fluoride compound comprises ammonium bifluoride, ammonium fluoride, or a combination thereof.

As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include their plural referents unless the context clearly dictates otherwise. The terms “containing” or “including” are intended to be synonymous with the term “comprising”, meaning that at least the named compound, element, particle, or method step, etc., is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, etc., even if the other such compounds, material, particles, method steps, etc., have the same function as what is named, unless expressly excluded in the claims.

In one aspect, the invention provides a composition comprising:

(a) phosphoric acid;

(b) at least one silane chosen from (i) alkylamino alkoxysilanes and (ii) alkylamino hydroxyl silanes, wherein said silane possesses at least one moiety chosen from alkoxy, hydroxyl, and fluoro;

(c) a solvent comprising water; and optionally

(d) a fluoride compound, provided that the fluoride compound is other than hexafluorosilicic acid.

In certain embodiments, the phosphoric acid will be present in the composition in about 50 to about 95 weight percent. In other embodiments, phosphoric acid will be present in about 70 to about 90 weight percent, and in other embodiments, about 85 weight percent.

In certain embodiments of the invention, the composition may further comprise a fluoride compound. In one embodiment, the fluoride compound is selected from HF and monofluoro phosphoric acid. In other embodiments, the fluoride compound is selected from cesium fluoride and potassium fluoride. In other embodiments, the fluoride compound is selected from ammonium hexafluorophosphate; tetramethylammonium hexafluorophosphate;

ammonium fluoride; ammonium bifluoride; fluoroboric acid; quaternary ammonium tetrafluoroborates and quaternary phosphonium tetrafluoroborates having the formula NR′₄BF₄ and PR′₄BF₄, respectively, wherein R′ may be the same as or different from one another and is selected from hydrogen, straight-chained, branched, or cyclic C₁-C₆ alkyl, and straight-chained or branched C₆-C₁₀ aryl; tetramethylammonium tetrafluoroborate (TMA-BF₄); and combinations thereof.

In certain embodiments, the alkylamino alkoxysilane and alkylamino hydroxyl silane compounds are represented by the formula

wherein each X is independently chosen from fluorine, a C₁-C₈ alkyl group, or a group of the formula —OR, wherein R is hydrogen or a C₁-C₈ alkyl group, n is an integer of from 1 to 6, and each R¹ is independently chosen from hydrogen, a C₁-C₈ alkyl group, or a group of the formula C₁-C₈ alkoxy(CH₂)_(n)—. In certain embodiments, the alkylamino alkoxysilane and alkylamino hydroxyl silane compounds are chosen from (3-aminopropyl)triethoxy silane (CAS No. 919-30-2); (3-aminopropyl)silane triol (CAS No. 58160-99-9); 3-aminopropyldimethylethoxysilane (CAS No. 18306-79-1); 3-aminopropylmethyldiethoxysilane (CAS No. 3179-76-8); and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (CAS No. 3069-29-2); (N,N-dimethyl-3-amnopropyl)trimethoxysilane, (CAS No. 2530-86-1); and 3-aminopropyldimethylfluorosilane (CAS No. 153487-58-2).

In certain embodiments, the alkylamino alkoxysilane and alkylamino hydroxyl silane compounds are represented by the formula

wherein each X is independently chosen from fluorine, a C₁-C₈ alkyl group, or a group of the formula —OR, wherein R is hydrogen or a C₁-C₈ alkyl group, n is an integer of from 1 to 6, y is an integer of from 1 to 6, and wherein z is an integer of from 1 to 6.

In certain embodiments, the alkylamino alkoxysilane and alkylamino hydroxyl silane compounds are chosen from N-(3-trimethoxysilylpropyl)diethylenetriamine (CAS Number 35141-30-1); N-(2-aminoethyl)-3-aminopropyltriethoxy silane (CAS No. 5089-72-5); N-(2-aminoethyl)-3-aminopropyl silane triol (CAS No. 1760-24-3); (3-trimethoxysilylpropyl)dethylenetriamine (CAS No. 35141-30-1); and N-(6-aminohexyl)aminopropyltrimethoxysilane (CAS No. 51895-58-0).

In certain embodiments, two alkylamino groups are connected to a silicon atom that carries two X groups (as defined above) or one X and one alkyl group, e.g. 3,3′-(dimethoxysilylene)bis-(1-Propanamine) (CAS No. 51749-36-1):

In certain embodiments, one or more aminoalkyl groups branch out of an alkyl or aminoalkyl chain that is connected to a silicon atom that carries three X groups (as defined above) or two X and one alkyl group, e.g. 2-[(Dimethoxymethylsilyl)methyl]-butanediamine (CAS No. 1019109-96-6):

In certain embodiments, two or more silicon atoms connected by oxygen bridges carry a total of at least one aminoalkyl group and at least one “X” group as described above, with the remaining silicon substituents being alkylamine, “X”, or alkyl; e.g. 1,3-Bis(3-aminopropyl)-1,1,3,3-tetraethoxydisiloxane (CAS No. 17907-78-7):

and its methoxy analog, 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethoxydisiloxane (CAS No. 76712-65-7):

The amount of the alkylamino alkoxysilane and alkylamino hydroxyl silane compounds in the compositions of the invention can be an amount that, in combination with the other materials of an etching composition, will provide desired etching performance, including desired silicon nitride etch rate and selectivity. For example, an etching composition can contain an amount of alkylamino alkoxysilane and alkylamino hydroxyl silane compounds, which may be a single species or a combination of two or more species, in a range from about 20 to 10,000 parts per million (i.e., from 0.0020 to 1.0 weight percent) based on total weight of the composition, or from about 20 to 2,000, 4,000, or 5,000 parts per million (i.e., from 0.002 to 0.2, 0.4, or 0.5 weight percent) based on total weight of the composition.

Component (c) is a solvent comprising water. Optionally, the solvent may further comprise one or more water-miscible solvents such as pyrrolidinones, glycols, amines, and glycol ethers, including, but not limited to, methanol, ethanol, isopropanol, butanol, and higher alcohols (such as C₂-C₄ diols and C₃-C₄ triols), tetrahydrofurfuryl alcohol (THFA), halogenated alcohols (such as 3-chloro-1,2-propanediol, 1-chloro-2-propanol, 2-chloro-1-propanol, 3-chloro-1-propanol, 3-bromo-1,2-propanediol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-iodo-1-propanol, 4-chloro-1-butanol, 2-chloroethanol), acetic acid, propionic acid, trifluoroacetic acid, N-methylpyrrolidinone (NMP), cyclohexylpyrrolidinone, N-octylpyrrolidinone, N-phenylpyrrolidinone, methyldiethanolamine, dimethyl formamide (DMF), dimethylsulfoxide (DMSO), tetramethylene sulfone (sulfolane), phenoxy-2-propanol (PPh), propriophenone, ethyl lactate, ethyl acetate, ethyl benzoate, acetonitrile, ethylene glycol, propylene glycol (PG), 1,3-propanediol, butyryl lactone, butylene carbonate, ethylene carbonate, propylene carbonate, dipropylene glycol, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobulyl ether, diethylene glycol monobulyl ether (i.e., butyl carbitol), triethylene glycol monobulyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether (DPGME), tripropylene glycol methyl ether (TPGME), dipropylene glycol dimethyl ether, dipropylene glycol ethyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether (DPGPE), tripropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-butyl ether, propylene glycol phenyl ether, dipropylene glycol methyl ether acetate, tetraethylene glycol dimethyl ether (TEGDE), dibasic ester, glycerine carbonate, N-formyl morpholine, triethyl phosphate, and combinations thereof. When using an alkoxysilane additive, its hydrolysis generates a small amount of alcohol, for example, methanol or ethanol, which is incorporated into the formulation as the alcohol itself or as its phosphoric acid monoester and is mostly boiled off at typical process temperatures. In addition, the organic solvent may comprise other amphiphilic species, i.e., species that contain both hydrophilic and hydrophobic moieties similar to surfactants.

In certain embodiments, the compositions of the invention further comprise low molecular weight amines and amine phosphate salts. In other embodiments, the low molecular weight amines and amine phosphate salts are primary, secondary, or tertiary C₁-C₆ alkylamine or phosphate salts thereof. Examples include dimethylamine, trimethylamine, triethylamine, tripropylamine, tributylamine and the like. It will be appreciated that when such amines or their aqueous solutions are added to a concentrated H₃PO₄ composition, amine phosphate salts will form.

In one embodiment, the composition comprises: (a) phosphoric acid; (b) N-(2-aminoethyl)-3-aminopropyl silanetriol; and (c) a solvent comprising water. In a further embodiment, the composition further comprises HF or monofluorophosphoric acid. In a further embodiment, the composition further comprises triethylamine or a dihydrogen phosphate salt thereof.

The composition may optionally comprise surfactant(s) (different from the other optional or required ingredients of the present description) to improve performance of the composition. As used herein the term “surfactant” refers to an organic compound that lowers the surface tension (or interfacial tension) between two liquids or between a liquid and a solid, typically an organic amphiphilic compound that contains a hydrophobic group (e.g., a hydrocarbon (e.g., alkyl) “tail”) and a hydrophilic group. Preferred surfactants are thermally stable and stay ionic under strongly acidic conditions such as the conditions of an etching process of the present invention. Examples include perfluoroalkylsulfonic acids and long-chain quaternary ammonium compounds (e.g. dodecyltrimethylammonium hydrogen sulfate). Fluorinated non-ionic surfactants such as Chemours' Capstone® FS-31/FS-35 can also be used. Non-ionic unfluorinated surfactants such as poly(ethylene glycol)-poly(propylene glycol) copolymers (“PEG-PPG”) can also be used, and are better suited for lower-acidity compositions (e.g. ≤75% H₃PO₄) and operation at ≤130° C.

The amount of surfactant in the composition can be an amount that, in combination with the other materials of an etching composition, will provide desired overall performance. For example, the composition can contain an amount of surfactant that may be in a range from about 0.001 to about 10 weight percent, e.g., from about 0.01 to about 0.5, 1, 2, 7, or 7 weight percent surfactant based on total weight of the composition.

Optionally, the compositions can contain an amount of carboxylic acid compound, meaning an organic compound that contains at least one carboxylic acid group. According to the invention, the presence of a carboxylic acid compound in composition as described can improve performance by inhibiting redeposition of silicon oxide or formation of particles of the same. In certain embodiments, the carboxylic acid compounds for use in the compositions include acetic acid, malonic acid, succinic acid, 2-methylsuccinic acid, glutaric acid, adipic acid, salicylic acid, 1,2,3-propanetricarboxylic acid (a.k.a. tricarballylic acid), 2-phosphonoacetic acid, 3-phosphonopropanoic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), any of which may be used alone, in combination together with each other, or in combination with a different carboxylic acid compound.

The amount of carboxylic acid compound (including derivatives thereof) contained in the compositions can be an amount that, in combination with the other materials of the compositions, will provide desired etching performance while not otherwise affecting performance or chemical stability of an etching composition. For example, the compositions can contain an amount of carboxylic acid compound, which may be a single species or a combination of two or more species, in a range from about 0.01 to about 10 weight percent based on total weight of the composition, or from about 0.1 to about 5 or 8 weight percent based on total weight of the composition.

The composition may contain water from one or from multiple sources. For example, water will be present in an aqueous phosphoric acid ingredient. Additionally, water may be used as a carrier for one or more of the other ingredients of the etching composition, and water may be added alone as its own ingredient. The amount of water should be sufficiently low to allow the composition to exhibit desired or preferred or advantageous etching performance properties, including a useful (sufficiently high) silicon nitride etch rate. An increase in the presence of water tends to increase the etch rate of silicon nitride but can also depress the boiling point of the etching composition, which forces a reduction in operating temperature of the etching composition and an opposite effect. Examples of amounts of water, from all sources, in an etching composition, can be less than about 50, 40, or 30 weight percent, for example in a range from about 5 weight percent to about 25 percent by weight, based on total weight of the composition, or in a range from about 10 to 20 weight percent water based on total weight of the composition.

Optionally, these and other example compositions as described can contain, consist of, or consist essentially of the phosphoric acid, the amino hydroxyl silane or amino alkoxy silane, and any one or any combination of the identified optional ingredients. Certain embodiments of the compositions of the invention do not require and may exclude other types of ingredients not typically included in an etching composition, such as a pH adjusting agent (other than the acids mentioned as potential ingredients herein) and solid materials such as abrasive particles.

The following table contains illustrative compositions in weight percent believed to be useful in the practice of the invention:

Ex- ample H₃PO₄ Solubilizer Active fluoride DIW Amine Total 1 71% APST, 1% HF, 0.2% 12.8% Dimethylamine, 15% 100% 2 76% N2APST, 1.5% 0 12.3% Trimethylamine, 10% 100% 3 74.4% APST, 3% NH4F, 0.2% 22.4% 0 100% 4 78% N3APTMS, 3% Triethylamine 18.5% 0 100% trihydrofluoride, 0.5% 5 82.5% APST, 1.2% 3-aminopropyl- 16% 0 100% dimethylfluorosilane 0.3% 6 78% N2APST, 2% MFPA, 0.5% 19% Triethylamine 100% dihydrogen phosphate (TEAP), 0.5 7 65% APTES, 2% 0 32% TEAP, 1% 100% 8 80% APTES, 1.25% Tetramethylammonium 18.3% TEAP, 0.3% 100% hexafluorophosphate, 0.15% 9 81.1% DMSBP, 2% HF, 0.2% 13.7% Dipropylamine, 3% 100% 10 82.2% BAPTEDS, 3% 0 14.8% 0 11 62% AHAPTMS, 3% Tetramethylammonium 26.8% 0 100% hexafluorophosphate, 0.2% DIW, 8% BC

As used herein, the following shorthand references are made:

-   (3-aminopropyl)triethoxy-silane (CAS No. 919-30-2) “APTES”; -   (3-aminopropyl)silane triol (CAS No. 58160-99-9) “APST”; -   N-(2-aminoethyl)-3-aminopropyl silane triol (CAS No. 1760-24-3)     “N2APST”; -   N¹-(3-Trimethoxysilypropyl)diethylenetriamine) “N3APTMS”; -   3,3′-(dimethoxysilylene)bis-(1-Propanamine) (CAS No. 51749-36-4)     “DMSBP”; 1,3-Bis(3-aminopropyl)-1,1,3,3-tetraethoxydisiloxane (CAS     No. 17907-78-7) “BAPTEDS”; -   N-(6-aminohexyl)aminopropyltrimethoxysilane (CAS No. 51895-58-0)     “AHAPTMS”; and diethylene glycol monobutyl ether (butyl carbitol)     “BC”.

In yet another aspect, the invention provides a method for removing silicon nitride from a microelectronic device, said method comprising contacting the microelectronic device with a composition of the present invention, for sufficient time under sufficient conditions to at least partially remove said silicon nitride material from the microelectronic device. For example, silicon nitride material may be removed without substantially damaging metal and metal silicide interconnect materials. The invention thus provides methods for selectively and substantially removing silicon nitride materials relative to polysilicon and/or silicon oxide materials from the surface of the microelectronic device having same thereon using the compositions described herein. The metal silicide materials that are present are not substantially corroded by said removal compositions using said method.

In etching application, the composition is applied in any suitable manner to the surface of the microelectronic device having the silicon nitride material thereon, e.g., by spraying the removal composition on the surface of the device, by dipping (in a static or dynamic volume of the removal composition) of the device including the silicon nitride material, by contacting the device with another material, e.g., a pad, or fibrous sorbent applicator element, that has the removal composition absorbed thereon, by contacting the device including the silicon nitride material with a circulating removal composition, or by any other suitable means, manner or technique, by which the removal composition is brought into removal contact with the silicon nitride material. The application may be in a batch or single wafer apparatus, for dynamic or static cleaning. In one embodiment, the application of the removal composition to the surface of the microelectronic device is controlled agitation whereby the composition is circulated through the container housing said composition.

The compositions of the present invention, by virtue of their selectivity for silicon nitride material relative to other materials that may be present on the microelectronic device structure and exposed to the composition, such as metallization, polysilicon, silicon oxide(s), etc., achieve at least partial removal of the silicon nitride material in a highly efficient and highly selective manner.

In use of the compositions of the invention for removing silicon nitride material from microelectronic device structures having same thereon, the composition typically is contacted with the microelectronic device structure for a sufficient time of from about 1 minute to about 200 minutes, in one embodiment, about 15 minutes to about 100 minutes, or about 1 minute to about 3 minutes for a single wafer tool, at sufficient conditions including, but not limited to, in one embodiment, a temperature in a range of from about 120° C. to about 180° C. Such contacting times and temperatures are illustrative, and any other suitable time and temperature conditions may be employed that are efficacious to at least partially remove the silicon nitride material from the device structure, within the practice of the invention.

Following the achievement of the desired removal action, the removal composition is readily removed from the microelectronic device to which it has previously been applied, e.g., by rinse, wash, or other removal step(s), as may be desired and efficacious in a given end use application of the compositions of the present invention. For example, the device may be rinsed with a rinse solution including deionized water and/or dried (e.g., spin-dry, N₂, vapor-dry, etc.).

The removal compositions of the invention selectively etch silicon nitride material relative to poly-Si and silicon oxides from the surface of the microelectronic device without causing substantial corrosion of the metal and/or metal silicide interconnect material(s). For example, the selectivity of silicon nitride to silicon oxide(s) in the presence of the removal compositions of the invention are, in one embodiment, in a range from about 10:1 to about 7,000:1, in another embodiment about 30:1 to about 3,000:1, and in another embodiment about 100:1 to about 2000:1 at temperatures of 40-100° C. in one embodiment, of 60-95° C. in another embodiment, and of 75-90° C. in yet another embodiment. When the silicic acid source includes an alkoxysilane, e.g., TEOS, the selectivity of silicon nitride relative to silicon oxide(s) can be tuned from about 20:1 to infinity in one embodiment and in the range from about 20:1 to about 7,000:1 in another embodiment. In fact, the selectivity is formally negative for some usable formulations, reflecting the fact that the thickness of the oxide film is very slightly but measurably increased by precipitation of silica.

An etching step of the present description can be useful to etch silicon nitride material from a surface of any type of substrate. According to particular embodiments, a substrate can include alternating thin film layers of silicon nitride as structural features of a substrate that includes alternating thin film layers of the silicon nitride layers with silicon oxide. The silicon oxide layers are high aspect ratio structures that contain the silicon nitride layers disposed between the layers of silicon oxide.

A still further aspect of the invention relates to methods of manufacturing an article comprising a microelectronic device, said method comprising contacting the microelectronic device with the compositions of the present invention for sufficient time to etchingly remove silicon nitride material from the surface of the microelectronic device having same thereon, and incorporating said microelectronic device into said article.

The compositions described herein are easily formulated by simple addition of the respective ingredients and mixing to homogeneous condition. Furthermore, the compositions may be readily formulated as single-package formulations or multi-part formulations that are mixed at the point of use, preferably multi-part formulations. The individual parts of the multi-part formulation may be mixed at the tool or in a storage tank upstream of the tool. The concentrations of the respective ingredients may be widely varied in specific multiples of the composition, i.e., more dilute or more concentrated, and it will be appreciated that the compositions described herein can variously and alternatively comprise, consist or consist essentially of any combination of ingredients consistent with the disclosure herein.

Another aspect of the invention relates to a kit including, in one or more containers, one or more components adapted to form the compositions described herein. In one embodiment, the kit includes, in one or more containers, the combination of at least one of components (a)-(c) above for combining with water at the fab or the point of use. The containers of the kit must be suitable for storing and shipping said cleaning composition components, for example, NOWPak®. containers (Advanced Technology Materials, Inc., Danbury, Conn., USA). The one or more containers which contain the components of the first cleaning composition preferably include means for bringing the components in said one or more containers in fluid communication for blending and dispense. For example, referring to the NOWPak®. containers, gas pressure may be applied to the outside of a liner in said one or more containers to cause at least a portion of the contents of the liner to be discharged and hence enable fluid communication for blending and dispense. Alternatively, gas pressure may be applied to the head space of a conventional pressurizable container or a pump may be used to enable fluid communication. In addition, the system preferably includes a dispensing port for dispensing the blended cleaning composition to a process tool.

Substantially chemically inert, impurity-free, flexible and resilient polymeric film materials, such as high density polyethylene, may be used to fabricate the liners for said one or more containers. Desirable liner materials are processed without requiring co-extrusion or barrier layers, and without any pigments, UV inhibitors, or processing agents that may adversely affect the purity requirements for components to be disposed in the liner. A listing of desirable liner materials include films comprising virgin (additive-free) polyethylene, virgin polytetrafluoroethylene (PTFE), polypropylene, polyurethane, polyvinylidene chloride, polyvinylchloride, polyacetal, polystyrene, polyacrylonitrile, polybutylene, and so on. Exemplary thicknesses of such liner materials are in a range from about 5 mils (0.005 inch) to about 30 mils (0.030 inch), as for example a thickness of 20 mils (0.020 inch).

Regarding the containers for the kits, the disclosures of the following patents and patent applications are hereby incorporated herein by reference in their respective entireties: U.S. Pat. No. 7,188,644 entitled “APPARATUS AND METHOD FOR MINIMIZING THE GENERATION OF PARTICLES IN ULTRAPURE LIQUIDS;” U.S. Pat. No. 6,698,619 entitled “RETURNABLE AND REUSABLE, BAG-IN-DRUM FLUID STORAGE AND DISPENSING CONTAINER SYSTEM;” and U.S. Patent Application No. 60/916,966 entitled “SYSTEMS AND METHODS FOR MATERIAL BLENDING AND DISTRIBUTION” filed on May 9, 2007 in the name of John E. Q. Hughes, and PCT/US08/63276 entitled “SYSTEMS AND METHODS FOR MATERIAL BLENDING AND DISTRIBUTION” filed on May 9, 2008 in the name of Advanced Technology Materials, Inc.

Accordingly, in a further aspect, the invention provides a kit comprising one or more containers having components therein suitable for removing silicon nitride from a microelectronic device, wherein one or more containers of said kit contains (a) phosphoric acid; (b) at least one silane compound chosen from (i) alkylamino alkoxysilanes and (ii) alkylamino hydroxyl silanes as described herein; and (c) a solvent comprising water; and optionally (d) a fluoride compound, provided that the fluoride compound is other than hexafluoro silicic acid.

This invention can be further illustrated by the following examples of certain embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLES

High aspect ratio structures were processed to first remove any oxidized film from the exposed silicon nitride. Structures were then processed in the formulation at the desired temperature in a boiling flask with stirring. For the conditions where silicate loading is specified either tetramethylammonium silicate (TMAS) or silica nanoparticles were added. For examples 16 and 17, TMAS was used and the loading is provided as ppm Si. For all other examples Sift nanoparticles were used and silicate loading is provided as ppm SiO₂. Structures were processed for times long enough to fully remove the SiN, typically between 45 minutes and 2 hours. After processing in the formulation structures were rinsed in hot deionized water and dried with flowing nitrogen. The etch rates shown were similarly obtained by processing blanket films, with thickness measured by spectroscopic ellipsometry.

TABLE 1 FORMULATION EXAMPLES (Weight Percent, balance ~85% H₃PO₄) Example

 / additive  

HF APST N2APST N3APTMS TEAP 12 0.0025 0.07 0.02 13 0.02 14 0.0025 0.04 0.02 15 0.04 0.02 16 0.002 0.09 17 0.002 0.07 18 0.002 1.4 0.2 Acronyms have the same meaning as for examples 1-11 above.

TABLE 2 Post-etch excess thickness (deposit build-up) of oxide in structure, as a function of added SiO₂ in the formulation (at 152° C.) 0 ppm 50 ppm 100 ppm 150 ppm 200 ppm Example SiO₂ SiO₂ SiO₂ SiO₂ SiO₂ 12 OK* OK OK OK OK 13 OK OK OK OK OK 14 OK OK  85% OK >2 nm >15 nm H₃PO₄ *”OK” signifies a change of <2 nm relative to the initial oxide thickness.

TABLE 3 Etch rates (ER) as a function of added SiO₂ (at 152° C.) Example 0 ppm 50 ppm 100 ppm 150 ppm 200 ppm 13 SiO₂ SiO₂ SiO₂ SiO₂ SiO₂ SiN ER 36 34 35 34 36 (A/min) ThOx ER 0.3 −0.1 −0.1 −0.2 −0.2 (A/min) 85% H₃PO₄ SiN ER 41 35 34 (A/min) ThOx ER 1.0 0.1 0.1 (A/min) Note that, compared with examples 12-14, 85% H₃PO₄ either has poor selectivity toward oxide (about 40:1 at 0 ppm silica, Table 3) or causes excessive oxide redeposition (at 100 and 200 ppm silica, Table 2).

TABLE 4 Performance Summary of Formulations 16 and 17: 3D NAND SiN Selective Etches 85% H3PO4/ 15% Example Critical H2O + Example Example 18 + require- [Si] = 16 + 80 17 + 45 45 ppm ments Target 40 ppm ppm Si ppm Si Si SiNx:SiO2 1000:1 830:1 >3000:1 2300:1 >:2000:1 Selectivity SiNx >12 12.5 14.6 14.5 12.5 Removal nm/min Rate Loading >0 ppm no 15-80 ppm 35-45 ppm 45->224 window Si window Si Si ppm (loading with selectivity >1000 & no re- deposition) Bath Life <10% √ stable ER stable ER stable ER Stability Change >24 hrs >24 hrs >24 hrs Shelf Life in ER √ >2 years >2 years >2 years Stability (Bath Loading life √ No ER No ER Not Stability >24 hrs, change, change, measured Shelf life no-redepo- no-redepo- ≥6 sition sition months) with with bleed/feed bleed/feed Temper- <160° C. 150° C. 150° C. 150° C. 150° C. ature (° C.) Addition of dissolved silicates during processing reduces silicon oxide etch rates without substantially changing nitride etch rate. At high enough dissolved silicate concentration a silica-rich precipitate is redeposited on SiO₂ surfaces within the 3D NAND structure. The loading window is defined in this case on the low end by where selectivity is >1000 and on the high end by the onset of redeposition. A different selectivity target will result in a different width of the loading window. 

We claim:
 1. A composition comprising: (a) phosphoric acid; (b) at least one silane chosen from (i) alkylamino alkoxysilanes and (ii) alkylamino hydroxyl silanes, wherein said silane possesses at least one moiety chosen from alkoxy, hydroxyl, and fluoro; (c) a solvent comprising water; (d) a fluoride compound, provided that the fluoride compound is other than hexafluoro silicic acid; and (e) an alkyl amine or phosphate salt thereof, wherein the alkylamino alkoxysilane and alkylamino hydroxyl silane compounds are represented by the formulas


2. The composition of claim 1, wherein the phosphoric acid is present in a range of 50 to 95 weight percent, based on the total weight of the composition.
 3. The composition of claim 1, wherein the fluoride compound is chosen from HF and monofluorophosphoric acid.
 4. The composition of claim 1, wherein the fluoride compound is chosen from cesium fluoride and potassium fluoride.
 5. The composition of claim 1, wherein the fluoride compound is chosen from fluoroboric acid; tetramethylammonium hexafluorophosphate; ammonium fluoride; ammonium bifluoride; quaternary ammonium tetrafluoroborates and quaternary phosphonium tetrafluoroborates having the formula NR′₄BF₄ and PR′₄BF₄, respectively, wherein R′ may be the same as or different from one another and is selected from hydrogen, straight-chained, branched, or cyclic C₁-C₆ alkyl, and straight-chained or branched C₆-C₁₀ aryl; tetrabutylammonium tetrafluoroborate (TBA-BF₄); and combinations thereof.
 6. The composition of claim 1 further comprising a surfactant, a carboxylic acid compound, or a dissolved silicate.
 7. A composition comprising: (a) phosphoric acid; (b) N-(2-aminoethyl)-3-aminopropyl-silane-triol or (3-aminopropyl)silane triol; (c) a solvent comprising water, (d) a fluoride compound, provided that the fluoride compound is other than hexafluoro silicic acid; and (e) an alkyl amine or phosphate salt thereof, wherein the alkyl amine or phosphate salt thereof is present and is chosen from triethylamine or a dihydrogen phosphate salt thereof.
 8. The composition of claim 7, wherein the fluoride compound is chosen from HF or monofluorophosphoric acid.
 9. The composition of claim 7 further comprising a surfactant, a carboxylic acid compound, or a dissolved silicate. 